The Onyx Forged blog

Articles written by the Onyx Forged design office: one question per article, answered with figures from our catalogue, our price list and the orders we deliver.

Do aftermarket wheels affect resale value? Keep the OEMs?
Guide
Valuation guides price a car as built, so aftermarket wheels rarely add their cost back, and a buyer may like them or not. What Auto Trader, the UK ombudsman, US total-loss rules and Australian and Canadian insurers say, and how to keep, declare, store or sell the original wheels.
Do aftermarket wheels void your car warranty?
Guide
In the US, a maker cannot make its warranty depend on its own branded wheels, but it can refuse a repair the wheels caused. The statute and FTC rule quoted word for word, the UK position from the 2023 block exemption and CMA guidance, Canada, Australia, Tesla, and what to do when a claim is refused.
Tire and wheel protection: what it covers, is it worth it?
Guide
A tire and wheel plan pays for tyres and wheels damaged by road hazards, with exclusions that decide most claims. What one published plan covers and leaves out, when it is a service contract and when it is insurance, the cancellation rights country by country, and what regulators found when they counted the claims.
Wheel and tire packages: what to check before you buy
Guide
A mounted package saves a fitting appointment, but it moves every fitment decision to the seller. The twelve checks to make before you pay, the rule behind each one in the US, Great Britain, New South Wales and Quebec, what changes for trucks and winter sets, and when a package is worth it.
Identify OEM wheels: style numbers and part numbers
Guide
An original wheel is identified by the car maker's part number, cast or stamped on the inside. A style number or design name is a sales label that can cover several sizes. Where to look, how to trace the number back to the car, what two maker documents show, and what a wheel without the number is likely to be.
What color rims for a white, black, grey or silver car?
Guide
Four neutrals make up about four cars in five. We measured how each wheel tone contrasts with each body colour, with the tyre and with brake dust, and set out what that means for a white, black, grey or silver car, the finish, and the rules in the UK, US, Canada and Australia.
Wheel styles explained: spokes, mesh, turbine, split-spoke
Guide
Seven families of wheel design, how to recognise each one, and what the design really changes: drag measured in a wind tunnel, brake cooling, cleaning, weight, the mounting side of a turbine wheel, and what UN Regulation No. 26 forbids on a wheel.
Curb rash on wheels: DIY kits, pro repair, prevention
Guide
Most curb rash is cosmetic, and a kit can hide it on a painted wheel. The limit is depth, not filler: about 1 mm into the metal. Diamond-cut and polished faces need a lathe or a polisher. What inspections in the UK, US, Australia and Canada say, what repair costs, and what rim protectors do.
How to paint rims at home: spray paint or Plasti Dip
Guide
Paint and Plasti Dip both work on a wheel at home, if you never coat the hub face, the nut seats, the centre bore or the bead seats. What the paint and dip makers' instructions say, the times between coats, how many cans for four wheels by our arithmetic, why the tyres are better off, and what the rules say in the UK, the US and Canada.
How to polish aluminum wheels: mirror or clear coat
Guide
Only bare aluminium can be polished to a mirror. How to tell bare metal from clear coat, what Alcoa, Kia, Mercedes-Benz, GM and the European wheel makers say, FEPA grit sizes set against a clear coat's thickness, pitted and kerbed wheels, the dust rules in the US, UK and Ontario, and how to protect the shine.
How to remove oxidation from aluminum wheels, by finish
Guide
White haze on a wheel is not always the same problem. Surface oxidation on bare aluminium polishes off; white worms under the lacquer do not; pits mean the finish is already gone. What General Motors, Nissan, a forged truck wheel maker, the European and Japanese wheel makers' associations say, finish by finish, with the acids to keep away from the wheel and the limits that call for a workshop or a new wheel.
Beadlock wheels: how they work and are they street legal?
Guide
A true beadlock clamps the tyre's outer bead between the wheel and a bolted ring, so the tyre stays put at very low pressure. No US federal standard names beadlocks, but Utah rejects those that do not meet SAE J2530, British Columbia rejects modified or welded rims, and one maker says its own are for off-highway use only. How they work, how to tell a simulated one, the rules country by country, and the bolt maintenance.
Carbon fiber wheels for cars: weight, strength, repair
Guide
Car makers that publish figures put a carbon wheel at 20 to 45 per cent lighter than the metal wheel it replaces. What that saving is worth, which tests exist for composite wheels, why brake heat matters, and why damage beyond the clear coat usually means a new wheel.
How forged wheels are made: billet, press, machining
Guide
A forged wheel starts as a solid aluminium billet, is pressed hot in a closed die, has its barrel formed, is heat treated to T6, and is machined to its final design and fit. The temperatures, the press forces, what each stage decides, and the tests a finished wheel faces in Japan, under UN Regulation No. 124 and in the United States.
Magnesium wheels: weight, corrosion, the fire myth, care
Guide
Porsche publishes 9 to 10 kg saved per set with forged magnesium wheels. Where the saving comes from, why the coating is the whole story for corrosion, what it takes to set solid magnesium alight, how to clean and repair them, and what the rules say in the UK, the US, Canada and Australia.
Center lock wheels: Porsche torque, care and conversions
Guide
A Porsche center lock wheel is held by one central nut or bolt tightened to 600 N·m (442.5 lb ft), not by five bolts at 160 N·m. What Porsche's own bulletins require when it is tightened, the 2024 US recall, the track-use replacement intervals, the safety pin, and what changes when a car is converted.
Wheel center caps: sizes by make, fitting and removal
Guide
There is no universal centre cap size, and the wheel's size in inches does not decide it. Six diameters read in the car makers' own shops (56, 65, 66, 66.8, 71 and 71.8 mm), what each one measures, how to measure your wheel, clip-in and floating caps, removal and refitting, and what the rules say in the UK, Europe, Australia, the US and Canada.
Wheel load rating: how much weight must a wheel carry?
Guide
The load a wheel must carry is half of its axle's maximum rating, read on the plate or the door-jamb label, not a quarter of the car's weight. How to work it out from GVWR and GAWR, where each country prints those numbers, how much margin the wheel tests build in, what a towbar adds, and the figures for a Tesla Model Y.
Wheel stud conversion: bolts to studs on BMW, VW, Audi
Guide
BMW, Volkswagen and Audi hold their wheels with bolts; a stud conversion swaps them for studs screwed into the hub and nuts. What changes, how much thread must engage, how to work out stud and bolt length, why the seat must match, whose torque applies, and what inspectors in the UK, the US and Australia look at.
17 vs 18 vs 19 inch wheels: ride, mpg and EV range
Guide
On twelve EPA pairs that differ only by wheel size, the bigger wheel lost about 4 to 16 per cent of range. Two magazine tests with identical wheel designs put the 17 inch first overall. What one inch changes in ride, braking, winter grip and paperwork, country by country.
Directional wheels: left and right, mounting, rotation
Guide
A directional wheel comes in a left and a right version, so each one can only go on its own side of the car. How to tell them apart, what that does to tyre rotation and to a directional tyre, what happens with the spare, and what the British MOT manual and UN Regulation No. 124 say.
Staggered vs square wheels: grip, rotation, AWD, wear
Guide
A staggered set has different sizes front and rear; a square set is the same at all four corners. Why carmakers stagger, what you give up in rotation and wear, the circumference limits that all-wheel drive imposes, our calculations, and what the UK, US, Australian and Canadian rules say.
Wheel fitment explained: flush, poke, tuck and stance
Guide
Fitment is where the tyre and rim sit against the edge of the wing. Flush, poke, tuck and stance put into millimetres from width, offset, tyre and camber, a way to measure your own car, and what the rules say about a tyre that sticks out, country by country.
Winter wheels: size down, steel or alloy, TPMS, storage
Guide
A second set of wheels for winter turns on four things: how small the brakes let you go, steel or alloy against road salt, what the pressure monitoring rules say in each country, and how to store the set. Each point is taken from the regulation, the car maker or the tyre maker.
How to mount a tire on a rim: lube, bead, seating pressure
Guide
A tyre comes off a rim fully deflated, goes back on with tyre lubricant, and seats its beads under a pressure ceiling: 40 psi in the US and Canada, 3.3 then 4.0 bar under the German standard. The steps from the tyre makers' and wheel makers' texts, the ceilings by country, the TPMS sensor, balancing, and what a home job cannot do.
Low profile tires: pros, cons, ride, potholes, rim damage
Guide
A low profile tyre has a sidewall under half its width. Sidewall heights calculated from 16 to 21 inches, what a carmaker, a tyre maker and a university study say about ride and potholes, why the load index matters more than the look, and the rules in the UK, US, Australia and Canada.
Stretched tires: are they safe, legal and insurable?
Guide
A tyre is stretched when its rim is wider than the widest one its maker lists. How far a typical stretch goes beyond the range, worked out from Continental's tables, what the MOT manual says about stretched tyres, the PSI question, bead-seating limits, the rules in four countries and what to tell your insurer.
Tire bead leak: corroded rims, causes and the fix
Guide
Most slow leaks at the bead come from the wheel: corrosion on the bead seat that you cannot see until the tyre is off. How to find the leak, what a car maker's bead seat repair involves, the limits it sets, why the wheel makers' association is stricter, porous cast wheels, and the rules in the UK, US, Australia and Canada.
Tyre valve stems: types, TPMS valves, when to replace
Guide
A valve stem is the small part that lets air in and keeps it there. Rubber snap-in valves, metal clamp-in valves and TPMS sensor valves, the pressure and speed limits in maker data, sensor nut torques from five documents, when to replace, why the cap matters, and what the UK, US, Canadian and Australian rules check.
Chain laws: California, Colorado and other US states
Guide
California's three chain levels, Colorado's traction law as revised in autumn 2025, Washington's and Oregon's signs, then British Columbia and the Australian Alps. What each text accepts as a tyre or a device, the tread depths converted to millimetres, the fines as published, and why big wheels can leave no room for a chain.
Winter tire laws in Quebec and BC: dates, studs
Guide
Quebec requires winter tyres on every registered car from 1 December to 15 March and accepts only the mountain-snowflake symbol or studs; British Columbia requires them only on signed highways, from 1 October to 30 April or 31 March, and accepts M+S. The legal texts, the 2026-2027 calendar, stud rules in Quebec, BC, Ontario and Washington State, fines and exemptions.
Track day checklist: wheels, tyres and brakes
Guide
What organisers check, and what they leave to you: hot tyre pressures from a tyre maker's data and what they imply, brake fluid boiling points under FMVSS 116 against a racing fluid's data sheet, wheel nut checks, kerbs and locking nuts, and the tread you need to drive home in the UK, US and Australia.
Car pulls to one side: driving, braking, after alignment
Guide
A pull that appears only under braking is not the same fault as one at a steady 60 mph. The causes sorted by when the car pulls, the tyre swap test from three maker procedures, our arithmetic on road camber and brake imbalance, and what the MOT and US, Canadian and Australian rules say.
How to clean alloy wheels and brake dust safely
Guide
Brake dust is mostly iron from the discs, baked on by heat. Clean the wheel cold, with a cleaner close to pH 7, rinse within the maker's time, and use an iron remover only by its label. What Nissan, Kia, GM, Land Rover and the Japanese wheel makers say, four safety data sheets compared, the acid mix that releases a toxic gas, care by finish, and the rules on wash water in the UK, US, Canada and Australia.
Powder coating vs painting wheels: durability and limits
Guide
Powder coat is tough, but it is cured at 154 to 210 °C, a range a powder maker says overlaps the one in which a wheel's alloy was hardened. What powder data sheets, a powder maker, Germany's refurbishment guideline, the European wheel makers and GM say, what a coating adds to a bead seat or a hub face, and what to ask before you pay.
Stuck lug nut or broken wheel stud: what to do
Guide
A seized wheel nut comes off with steady force from a hand tool, never a torch: tyre makers say never heat a wheel. A missing or broken stud fails inspection in Great Britain, Queensland, British Columbia and Hawaii. What causes seizing, the safe order of steps, stud replacement and refitting.
Worn shocks: symptoms, tests and tyre wear
Guide
Eight signs of worn shocks or struts, each tied to a source; what the published test figures on stopping distance actually say; how cupped tyres form; the bounce test and its limits; and the text of the MOT and a US state inspection.
All-terrain vs mud-terrain tyres: on road, noise, snow
Guide
All-terrain and mud-terrain are sales names; the sidewall says which rules apply. What the POR mark takes a tyre out of, what one maker's label data show for noise and fuel, which snow rules accept M+S and which want the mountain snowflake, and why an LT tyre carries its load index only at high pressure.
Do EV tires wear faster? HL load index, Tesla, data
Guide
The only field figure we could trace to its source shows EV tyres replaced about 26 % sooner on UK fleets, with a caution from the people who published it. Michelin says a purpose-built EV should wear like its petrol twin. Here is the data, the HL load index, Tesla's rotation rule, and what a label class is worth in range.
BMW star, Mercedes MO, Porsche N: OE tyre markings
Guide
The BMW star, Mercedes-Benz MO, Porsche N, Audi AO and Tesla T marks say that a tyre was developed or endorsed for one carmaker. No rule we read in the UK, the US, Australia or Canada requires them. A table of the markings with the source that defines each one, the same-axle rules country by country, and our calculation of what tread wear does to two tyres on one axle.
Semi-slick tyres: road legal? UK, US, Australia
Guide
No law defines a semi-slick. What makes one road legal is its approval mark: the E mark in the UK and Australia, the DOT symbol in the US. The texts country by country, what the tyre makers say about rain and warm-up, our reading of new tread depths and our hot-pressure calculation.
New tyres front or back? Replace 2 or 4 on AWD?
Guide
Two new tyres go on the rear axle, on front-, rear- and all-wheel drive. Why the tyre makers say so, the rare exceptions, how much tread difference an all-wheel-drive car tolerates, what to do with a staggered set-up, and the law in the UK, US, Australia and Canada.
Plug vs patch tire repair: what the rules allow
Guide
A string plug pushed in from outside gets you to a fitter; the repair the rulebooks accept is a plug that fills the hole and a patch that seals the liner, fitted with the tyre off the wheel. Where on the tread, how big a hole, what happens to the speed rating and to a run-flat, country by country.
Tire bulge on the sidewall: causes, is it safe?
Guide
A bulge on a tyre's sidewall means the cords inside have broken, usually after a kerb or pothole impact, and only rubber holds the air. What the tyre makers say, the exact MOT and inspection rules in the UK, Canada, Australia and the US, how to tell a bulge from a harmless dent, why it cannot be repaired, and what warranties cover.
Tyre wear patterns: what uneven wear means
Guide
Each wear pattern points to a family of causes: pressure, toe, camber, shocks, balance or a bent wheel. A table built from five makers' pages, where they disagree, when the wheel is the culprit, and the tread rules in the UK, the US, Australia and Canada.
Bedding in brake pads and rotors: procedures compared
Guide
Bedding in lays an even film of pad material on the disc. Nine published procedures side by side, from six gentle stops to fifty controlled ones, what the official test rules do, and the mistake that undoes it all: stopping and holding the pedal on hot brakes.
Ceramic vs semi-metallic brake pads: which is better
Guide
Neither pad is better in general: ceramic pads trade some bite and heat capacity for less noise and lighter dust, semi-metallic pads the reverse, and the first rule is the type your car was built with. The three things called ceramic, a table of what makers and testers say, the R90 equivalence test and the copper laws, by country.
Drilled vs slotted rotors: pros, cons, daily driving
Guide
Brembo says drilled and slotted discs offer comparable benefits; the difference is in cracking, pad wear and noise. What brake makers and carmakers publish, which cracks are normal and which are not, how much braking surface each design removes, and what the MOT and US inspections check.
Painting brake calipers on the car: method and paint
Guide
Calipers can be painted on the car, but the wheels come off and the car goes on axle stands. Heat ratings read in four product sheets, set against brake fluid boiling points, the surfaces that must stay bare, the masking, the cure, and how a colour shows through spokes.
Nitrogen in tires vs air: is it worth it?
Guide
Air is already 78 per cent nitrogen. In a year-long test, nitrogen-filled tyres lost 2.2 psi and air-filled ones 3.5 psi: a real difference, smaller than one cold morning. The tyre makers' association, Michelin and Continental say nitrogen is not needed on a car; aircraft over 75,000 lb are another matter.

The Onyx Forged blog

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